The aims of the proposed research program are to (a) develop a model describing the P-V relations of the left ventricle in terms of the viscoelastic properties of the myocardium, ventricular geometry, wall mass and external constraints, (b) obtain correction factors for ejection phase indices and (c) obtain stiffness-stress relations in pressure and volume overload ventricles of infant and young adult patients. Assuming an ellipsoidal model for the left ventricle and a constitutive equation for the myocardium, a differential equation for the P-V relation is to be obtained in terms of various parameters. Methods are to be developed for correcting indices such as Vcf, ejection fraction etc. for afterload, so that valid patient to patient comparisons can made. In order to study the effect of age on passive elastic stiffness of heart muscle and hypertrophy effects, infant and young adult patients will be studied and P-V relations obtained with the aid of echocardiography.